Remove Only One Duplicate from An Array

Question

I'm trying to only remove one of the 2s from an array, but my code removes all of them. My code is as follows:

var arr = [2,7,9,5,2]
arr.filter(item => ((item !== 2)));

and:

var arr = [2,7,9,2,2,5,2]
arr.filter(item => ((item !== 2)));

Both remove all the 2s. I thought about removing duplicates, where it works if there's only one duplicate - e.g.:

Array.from(new Set([2,7,9,5,2]));
function uniq(a) {
 return Array.from(new Set(a)) 
}

But fails if there's multiple duplicates as it just removes them all, including any other duplicated numbers:

Array.from(new Set([2,7,9,9,2,2,5,2]));
function uniq(a) {
 return Array.from(new Set(a)) 
}

Does anyone know how to only remove one of the 2s? Thanks for any help here.

Answer 1

You could use indexOf method in combination with splice.

var arr = [2,7,9,5,2]
var idx = arr.indexOf(2)
if (idx >= 0) {
    arr.splice(idx, 1);
}
console.log(arr);

Answer 2

You could take a closure with a counter and remove only the first 2.

var array = [2, 7, 9, 2, 3, 2, 5, 2],
    result = array.filter((i => v => v !== 2 || --i)(1));
    
console.log(result);

For any other 2, you could adjust the start value for decrementing.

var array = [2, 7, 9, 2, 3, 2, 5, 2],
    result = array.filter((i => v => v !== 2 || --i)(2));
    
console.log(result);